Certain structures need to be protected from access by unauthorized personnel. Examples of such structures include, but are not limited to, personal residences, vacation homes, garages, isolated buildings, cell tower sites, schools, businesses, prisons, and office buildings. Occasionally, a mere physical lock on the structure will not prevent an intruder from forcing access to the structure. Even an audible alarm may not be a sufficient deterrent if the structure is, for example, located in a remote area. For example, intruders enter onto a cell tower site, break into the site, and steal copper from the cell tower site. Other deterrence means are needed either to prevent the intruder from accessing the structure or doing much inside it once accessed, or to mark the intruder for later identification.
In many cases, the need for such protection has not been anticipated. For example, the epidemic of copper theft is a relatively new phenomenon. The need to protect important infrastructure from terrorist activities has only recently become apparent. As a result, many important resources are still protected only by simple doors.